In fact, the Castle star has at the ready, on his iPhone, a whole list of things he has yet to do as an actor, yet aspires to. Someday.

“Land a plane…. Play my own double…. Hit a detonator button…,” he rattles off from his “to-do” list — in response to a TVLine reader’s question — during my visit to the ABC drama’s set. Continuing on: “Use a dynamite plunger…. Walk away from an explosion, in slow motion…. Defuse a bomb…..” Fillion stops, then reaches his thumb for the backspace button. “Actually, I can scratch that last one off. I did that,” in last season’s Castle episode, “Still.”

THE MARRYING MAN? | As mystery novelist Richard Castle, Fillion has in fact helped his partner in crimefighting, Kate Beckett (played by Stana Katic), “defuse” all sorts of intense situations. But as Season 5 drew to a close, the proverbial fuse was burning on their biggest collaboration of all: romance.

To recap: For four years, Castle and his NYPD detective muse indeed danced around their ever-increasing feelings for one another, ultimately caving in to their desires in the Season 4 finale. Last season then found them trying, with some (albeit ephemeral) success, to keep their relationship under wraps at the 12th precinct. It all built to last May’s season finale, in which Castle blindsided his love with a ring and a question: “Katherine Houghton Beckett — will you marry me?”

Getting Rick on bended knee wasn’t easy, the way Season 5 winded down. In fact, for a stretch there, viewers — and Kate herself — had to wonder if he was going to go the other way with his swing set speechifying and bail on their relationship. After all, a prior episode found Kate calling into question Rick’s appreciation of her, priming the head-turning cop for a pass from a dashing wannabe suitor (played by Ioan Gruffudd in the episode “The Squab and the Quail”).

While some were quick to carp that those obstacles weren’t organic, that Kate’s concerns about Rick’s commitment did not jibe with the fact that he sat on a bomb with her, Fillion appreciates the need for friction.

“When you’re watching television, you tend to want for a fairytale. But what we, I think, are experiencing on Castle is more reality-driven,” he offers. “These things happen in real life. These. Things. Happen. All the time. People make decisions in the moment that have repercussions, and it doesn’t seem like a big deal in the moment, but the repercussions are there. That is real life.”

CASTLE PULLS THE TRIGGER | Reflecting on Rick’s ultimate play there at the playground, Fillion says, “It seemed like a natural progression,” adding that the show’s creator Andrew W. Marlowe and the writers “have been very artful” over the years “with the ‘Will they, won’t they,’ they will, where will it go from here” dynamic between the lead characters.

“It’s a bit of a dance,” he observes, “because when you’ve got a successful television program that’s doing well, you don’t want to mess with it too much, you don’t want any jarring changes, I don’t think. And they’ve been very artful with it.”

For Castle — who hasn’t the best track record as a husband and has never lacked female company — proposing marriage was testament to a new maturity. Yet when I ask Fillion if it made him “feel good” to see Rick take that step, as the man who plays the pretend author, he politely waves off the suggestion.

“I really don’t think of it in those terms. I think of it more in terms of the well-being of the show,” he counters. “I mean, I come to work every day and I don’t really think, ‘What’s in it for me?’ This is a real team effort, and when you’re here every day, when there’s 60 guys here and we’re all doing the same thing, and we’re all plugging away — and a lot of people here are working a lot harder than I am — I tend to think of it in terms of the well-being of the show.”

How that bended-knee business plays out for Rick and his would-be fiancee, Fillion of course can’t say. That’s what the Season 6 premiere, airing Monday at 10/9c, will reveal. Show boss Marlowe, meanwhile, teases that while the writers “toyed with” a few different outcomes, ultimately “we’re always looking for what’s most honest and what’s going to be most challenging. And with where the characters were in the finale, [the path they choose] is honest.”

ROLES OF A LIFETIME | At the time I spoke with Fillion – sitting across from each other in the 12th’s interrogation room, natch, as his ABC series was lensing Episode 3 — he had quite a summer already behind him. His Firefly boss Joss Whedon’s art house effort Much Ado About Nothing had been released two months prior. Monsters University, in which he cannily voiced a chest-puffing frat house stud, had just hit theaters. And Percy Jackson: Sea of Monsters, where he played the messenger god Hermes, was on its way to the Cineplex. All that, and a whole season of Castle capers in front of him.

So I must ask: “Is this the most satisfied you have ever been as an actor?”

“I’m having a really good time,” he states, grinning. “I’m always amazed that I’m continually invited to participate in projects that I’m thrilled about being a part of.

“I never really dreamed about being a waiter, but I was a waiter for years. And plugging away at a job like that is fine, but it’s not my dream,” he adds. “Now all my jobs are dream jobs. It’s a good feeling.”